Embryonal Rhabdomyosarcoma: Understanding Your Pathology Report

Section Editor: Bibianna Purgina MD FRCPC
September 19, 2026

Embryonal rhabdomyosarcoma is a type of cancer that develops from cells that would normally become skeletal muscle. Skeletal muscle is the muscle that moves the arms, legs, and other parts of the body. It is a type of sarcoma, a cancer that begins in the body’s connective tissues.

Embryonal rhabdomyosarcoma is the most common type of rhabdomyosarcoma, making up about 60% to 70% of cases. Other types include alveolar, spindle cell/sclerosing, and pleomorphic rhabdomyosarcoma.

It mainly affects children, most often those under age 10. The most common locations are the head and neck and the urinary and reproductive organs. It can also start in the arms, legs, or trunk. Compared with alveolar rhabdomyosarcoma, embryonal rhabdomyosarcoma has a more favorable outlook.

This article explains how embryonal rhabdomyosarcoma is diagnosed and what the pattern, margins, lymph nodes, and stage in your pathology report mean.

What causes embryonal rhabdomyosarcoma?

Embryonal rhabdomyosarcoma develops when immature muscle cells collect genetic changes that keep them dividing instead of maturing. The changes usually involve many genes rather than a single defining change. Genes in the RAS family are among the most commonly affected.

Unlike alveolar rhabdomyosarcoma, embryonal rhabdomyosarcoma does not have a FOXO1 fusion. A fusion is an abnormal joining of two genes that are normally separate. Showing that no FOXO1 fusion is present is an important part of making this diagnosis.

Most children with embryonal rhabdomyosarcoma have no inherited condition. In a small number, the cancer develops in a child with a syndrome that raises cancer risk. These include Li-Fraumeni syndrome, Beckwith-Wiedemann syndrome, Costello syndrome, Noonan syndrome, neurofibromatosis type 1, and DICER1 syndrome. Your team may suggest genetic counseling if the tumor or the family history points to one of these conditions.

What are the symptoms of embryonal rhabdomyosarcoma?

The symptoms of embryonal rhabdomyosarcoma depend on where the tumor starts. Because the tumor can grow quickly, symptoms often develop over weeks to months:

Head and neck. A lump, a blocked nose, nosebleeds, trouble swallowing, or a bulging eye.
Urinary and reproductive organs. Trouble passing urine, blood in the urine, a lump in the abdomen, or in girls, tissue that protrudes from the vagina.
Arms, legs, or trunk. A lump or swelling, pain, or difficulty moving the affected area.
Near the spine or in the pelvis. Numbness, weakness, or difficulty walking.

How is the diagnosis made?

The diagnosis of embryonal rhabdomyosarcoma is made after a pathologist examines a sample of the tumor under the microscope. The sample is usually obtained by a biopsy, using a needle or a small incision. In some cases, the surgeon removes the whole tumor during the first operation.

Under the microscope, embryonal rhabdomyosarcoma is made of immature muscle cells called rhabdomyoblasts. These cells have small, round, dark nuclei, and the nucleus is often pushed to one side of the cell. More mature tumor cells have more pink cytoplasm, which is the body of the cell. These cells may take on a long, strap-like shape. The tumor usually contains crowded areas next to looser areas, and many of the cells are dividing.

Molecular testing shows that no FOXO1 fusion is present. This is done with FISH, which uses glowing probes to show whether the FOXO1 gene has broken apart, or with next-generation sequencing (NGS). A negative result supports the diagnosis of embryonal rhabdomyosarcoma and rules out the alveolar type, which is treated differently.

Once embryonal rhabdomyosarcoma is confirmed, imaging tests show how far the tumor has spread. These usually include MRI of the area where the tumor started and CT scans of the chest, abdomen, and pelvis. The next section describes the immunohistochemistry tests used to confirm the diagnosis.

Immunohistochemistry

Immunohistochemistry uses antibodies to show which proteins tumor cells make. For embryonal rhabdomyosarcoma, it confirms that the tumor cells are developing skeletal muscle cells. Your report may include some of the following:

Desmin. This muscle protein is positive in embryonal rhabdomyosarcoma.
Myogenin. This protein is found only in developing skeletal muscle cells. In embryonal rhabdomyosarcoma, it is usually positive in only some of the tumor cells. Strong staining in nearly every cell would point toward alveolar rhabdomyosarcoma.
MyoD1. This protein is also found in developing skeletal muscle. It is usually positive, and staining must be nuclear to count as a positive result.

These stains confirm that the tumor is a rhabdomyosarcoma. They cannot show whether a FOXO1 fusion is present, which is why molecular testing is also performed.

Histologic pattern

Your report may describe a specific pattern within the embryonal rhabdomyosarcoma. These patterns do not change the diagnosis, but you may see the words on your report:

Botryoid. This pattern forms grape-like bumps under the lining of a hollow organ, such as the vagina, bladder, nose and throat, or bile ducts. Botryoid tumors make up about 10% of all rhabdomyosarcomas. In a large study of children, they had slightly better outcomes than other embryonal tumors, although the difference disappeared once site, surgery, and spread were accounted for.
Anaplastic. This pattern contains scattered very large, oddly shaped tumor cells. It is sometimes seen in children with Li-Fraumeni syndrome. Studies have not shown that anaplasia by itself changes the outcome.

Histologic grade

Pathologists do not assign an FNCLCC grade to embryonal rhabdomyosarcoma. All types of rhabdomyosarcoma are treated as high-grade cancers, so your report will usually not include a grade. A report without a grade is not incomplete.

Tumor size

Tumor size is the greatest dimension of the embryonal rhabdomyosarcoma, measured in centimeters (cm). The size may come from imaging or from the tumor removed at surgery. Tumors 5 cm or smaller are associated with a more favorable outcome, and size is used to assign stage.

Tumor extension

Tumor extension describes whether embryonal rhabdomyosarcoma has grown into nearby structures such as muscle, bone, nerves, blood vessels, or organs. After removing the tumor, the pathologist examines the surrounding tissue and reports which structures contain tumor cells. A tumor that has grown into nearby structures is described as invasive, and this affects both the stage and the plan for surgery and radiation.

Treatment effect

Many children with embryonal rhabdomyosarcoma receive chemotherapy, and sometimes radiation therapy, before surgery. When the tumor is removed after this treatment, the pathologist examines it to see whether living tumor cells remain.

For rhabdomyosarcoma, no specific percentage of dead tumor is used to guide treatment. Your team judges the response to treatment mainly with imaging and interprets the pathology findings alongside those results.

Lymphovascular invasion

Lymphovascular invasion means that cells from the embryonal rhabdomyosarcoma are seen inside a small blood vessel or lymphatic channel. These vessels give cancer cells a route to lymph nodes and other parts of the body.

Present. Tumor cells were seen inside a vessel. This finding is associated with a higher risk of tumor spread.
Not identified. No tumor cells were seen inside vessels in the tissue examined.

Perineural invasion

Perineural invasion means tumor cells are growing around or along a nerve. A pathologist may mention it when it is seen in embryonal rhabdomyosarcoma. When present, it suggests the tumor may extend beyond its visible edge and may raise the risk of the tumor coming back in the same place.

Surgical margins

Margins are the edges of tissue cut by the surgeon to remove an embryonal rhabdomyosarcoma. The pathologist inks these edges and examines them under the microscope.

Negative margin. No tumor cells are seen at the inked edge. The report may also give the distance between the tumor and the closest margin.
Positive margin. Tumor cells reach the inked edge, and some tumor may have been left behind. Further surgery or radiation therapy may be considered.

Margins are only reported when the tumor was removed rather than sampled. For many rhabdomyosarcomas, complete removal at the first operation is not possible without harming an important structure. In those situations, a biopsy alone is the correct first step, and chemotherapy and radiation are used to control the tumor.

Lymph nodes

Lymph nodes are small immune organs found throughout the body, and rhabdomyosarcoma can spread to the nodes near where it started. Embryonal rhabdomyosarcoma reaches lymph nodes less often than the alveolar type.

For tumors of the arms and legs, and for tumors beside the testicle in boys aged 10 and older, nodes may be checked even when imaging looks normal. When nodes are removed, the report lists how many were examined and how many contain tumor cells. Tumor found in a lymph node raises both the stage and the risk group.

Biomarker and molecular testing

For embryonal rhabdomyosarcoma, no biomarker test currently selects a specific targeted drug. The molecular test for a FOXO1 fusion is diagnostic, and a negative result is expected for this diagnosis. The treating team also uses that result to assign the risk group.

When the cancer comes back or does not respond to treatment, the tumor may be tested with a broad NGS panel. This test looks for changes that could make a child eligible for a clinical trial. Some tumors have a DICER1 change, which may point to an inherited condition and lead to genetic counseling. You can learn more about tumor testing in our Biomarkers and Genetic Testing section.

Stage, clinical group, and risk group

Rhabdomyosarcoma in children, including embryonal rhabdomyosarcoma, is described by three separate systems. All three may appear in the medical record.

Stage, from 1 to 4. This is based on where the tumor started, its size, whether lymph nodes are involved, and whether it has spread to distant sites. Sites are divided into favorable and unfavorable. Favorable sites include the area around the eye, the head and neck away from the lining of the brain, and the biliary tract. They also include the urinary and reproductive organs, except the bladder and prostate.
Clinical group, from I to IV. This is based on how much tumor was removed at the first operation. Group I means the tumor was completely removed. Group II means small amounts remained or a lymph node was involved. Group III means visible tumor remained, which includes tumors that were only biopsied. Group IV means the tumor had already spread to distant sites.
Risk group: low, intermediate, or high. This combines stage, clinical group, FOXO1 fusion status, and age and site. The risk group determines treatment intensity.

The pathology report provides several of these ingredients but usually does not state the risk group itself. The treating team assigns it once the imaging, surgery, and molecular results are available. Because embryonal rhabdomyosarcoma has no FOXO1 fusion, many children with this diagnosis fall into the low or intermediate risk groups.

In adults, the pathology report may instead include a pathologic stage (pTNM) from the American Joint Committee on Cancer (AJCC), 8th edition. For tumors of the arms, legs, and trunk, the tumor stage (pT) is based on size. Other body sites use different rules.

pT1. The tumor is 5 cm or smaller.
pT2. The tumor is larger than 5 cm but not larger than 10 cm.
pT3. The tumor is larger than 10 cm but not larger than 15 cm.
pT4. The tumor is larger than 15 cm.

The nodal stage for adults is pN0 if no tumor cells were found in the lymph nodes examined and pN1 if tumor cells were found. If no lymph nodes were removed, the report will usually say that pN was not assigned.

What is the prognosis?

Embryonal rhabdomyosarcoma has a more favorable outlook than alveolar rhabdomyosarcoma. In a study of 2,192 children with embryonal rhabdomyosarcoma treated in cooperative group trials, about 73% were disease-free five years after diagnosis. Children with botryoid tumors did slightly better, at about 80%.

Outcomes are best for small tumors at favorable sites that are completely removed. Survival is considerably lower when the cancer has already spread at diagnosis. These numbers describe groups of children and cannot predict what will happen in one child.

Features associated with the outcome of embryonal rhabdomyosarcoma include:

Spread at diagnosis. This is the strongest predictor of a less favorable outcome.
Primary site. Tumors at favorable sites, such as the area around the eye, do better than tumors at unfavorable sites. Unfavorable sites include those next to the lining of the brain and those in the bladder and prostate.
Tumor remaining after surgery. A higher clinical group is associated with a less favorable outcome.
Tumor size. Tumors larger than 5 cm do less well than smaller tumors.
Lymph node involvement. Tumor in nearby nodes is associated with a less favorable outcome.
Age. Children between 1 and 9 years old tend to do better than infants, adolescents, and adults.

What happens after the diagnosis?

After embryonal rhabdomyosarcoma is confirmed, a team that includes an oncologist, surgeon, radiation oncologist, and pathologist usually plans care. The findings in the pathology report, especially the margins, the lymph nodes, and the fusion result, are combined with imaging to assign the risk group and plan treatment.

Chemotherapy. Everyone with embryonal rhabdomyosarcoma receives chemotherapy because tumor cells may be present elsewhere in the body without being visible on scans. A common combination is vincristine, actinomycin D, and cyclophosphamide, adjusted by risk group.
Surgery. The tumor is removed with a rim of normal tissue when this can be done without unacceptable loss of function. At some sites, such as the area around the eye, surgery is intentionally limited to protect vision.
Radiation therapy. Radiation is used when tumor remains after surgery, when a margin is positive, or at sites where surgery cannot remove the tumor safely.
Clinical trials. Children are usually treated on a protocol developed by a cooperative research group, and trials should be discussed when the cancer comes back.

After treatment ends, follow-up with regular imaging continues for several years. Long-term follow-up also monitors chemotherapy and radiation effects on growth, fertility, and organ function.

Questions to ask your doctor

Was FOXO1 testing performed, and did it confirm that no fusion is present?
Was a botryoid or anaplastic pattern described in the report?
Where did the tumor start, and is that site considered favorable or unfavorable?
What stage and clinical group have been assigned, and what do they mean?
Which risk group does this fall into?
How large was the tumor, and did it grow into nearby structures?
Was the whole tumor removed, and were the margins negative?
Were any lymph nodes examined, and did any contain tumor?
Should we see a genetic counselor about an inherited condition?
Which chemotherapy regimen is recommended, and for how long?
Will radiation therapy be part of the plan?
What follow-up will be needed after treatment, and for how long?